1. Field of the Invention
This invention pertains generally to blood sensing, and more particularly to blood coagulation time and hematocrit level sensing.
2. Description of Related Art
The administration of anticoagulants has become a routine healthcare tool to prevent and combat a number of patient health problems. The prescription of oral anticoagulants (e.g. coumarins, direct thrombin inhibitors, etc.) is typically used as a long-term prophylaxis to prevent thrombosis in a number of “chronic” situations. For example, this includes patients with long-term health concerns such as atrial fibrillation, past episodes of embolism or stroke, inherited/acquired thrombophilic disorders, and surgeries such as those involving prosthetic heart valve replacement, coronary artery stent implantation, or orthopedic surgery (e.g. knee or hip replacements).
As a result of the widespread use of anticoagulants, 2.5 million Americans now rely on blood thinners annually. However, the most commonly used oral anticoagulants, coumarins, have a number of adverse side effects that require continual blood monitoring and alteration of the drug dosage administered to the patient. The activity of coumarins, which are vitamin K antagonists, responds to a number of factors such as diet (foods high in vitamin K, cranberries, green vegetables), liver, kidney, and thyroid dysfunction, alcohol, several herbs and spices, and many commonly used drugs such as aspirin and certain antibiotics. Consequently, in 2005 the International Self-Monitoring Association for Oral Anticoagulation reviewed and advocates for the increased practice of patient self-testing as a means to counter the variability in initial dose selection and stabilization, as well as long-term difficulties in maintaining anticoagulant stability. Among the benefits of self-monitoring were improved quality of life, greater cost-effectiveness, patient education, and a decreased risk of death from hemorrhage.
Unfortunately, the self-management of coagulation has not become a commonplace phenomenon as it has been with the use of glucose monitors to manage diabetes. A number of self-monitors are available on the market, such as the Roche CoaguChek and the HemoSense INRatio, yet these devices cost between $500-$2,000. In contrast, glucose monitors cost two orders of magnitude less and can generally be purchased for less than $20. A number of variables are at fault for this price differential. One aspect is that some coagulation monitors rely on more expensive technology like the CoaguChek, which detects the proteolytic cleavage of a fluorescent peptide. However, other monitors such as the INRatio, which electrochemically measures a change in impedance due to clot formation, are much cheaper and similar technologies to a glucose monitor, but still cost ˜$500.
It is suspected that slow user adoption has not created a sustainable market that can survive upon small profit margins, thus the exorbitantly inflated price of blood monitors. To compound this issue, patient self-testing occurs on a monthly to weekly basis. This is a stark contrast to diabetics who test on a daily basis, perhaps as many as 3-10 times per day, thus using more consumables. In order for the self-monitoring of blood coagulation to become widespread, a cheap and more basic product that emulates a pregnancy lateral flow assay may drastically improve adoption. Even though pregnancy tests are used infrequently, their simplicity and robustness enable widespread accessibility.
Accordingly, an object of the present invention is a blood coagulation chip with attributes that are more similar to a lateral flow assay than to a glucose monitor.